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Physics · 2022 · 3 marks
CBSE 2022 · Region 3 · Set 1 · Q7
In a diffraction pattern due to a single slit, how will the angular width of central maximum change, if (i) Orange light is used in place of green…
In a diffraction pattern due to a single slit, how will the angular width of central maximum change, if
(i)
Orange light is used in place of green light,
(ii)
the screen is moved closer to the slit,
(iii)
the slit width is decreased ? Justify your answer in each case.
Marking-scheme solution
Effect on angular width of central maximum in the three cases
In diffraction pattern the angular width of central maximum $\displaystyle =\frac{2 \lambda}{a}$ where $\displaystyle a$ is the slit width and $\displaystyle \lambda$ is the wavelength.
(i) Increases
$$\text { As } \theta=\frac{2 \lambda}{a} \text { and } \lambda_{\text {orange }}>\lambda_{\text {green }}
$$
(ii) No change / no effect
As $\displaystyle \theta$ does not depend upon the distance of the screen from the $\displaystyle \operatorname{slit}(D)$
(iii) Increases
As $\displaystyle \theta$ is inversely proportional to the slit width $\displaystyle (a)$.
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